1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.
2. Description of the Related Art
Charge-trapping nonvolatile semiconductor memory devices are being developed which uses a charge trapping charge storage insulating film as a charge storage layer (see Jpn. Pat. Appln. KOKAI Publication No. 2004-158810). In the charge-trapping nonvolatile semiconductor memory device, charges injected into the charge storage insulating film through a tunnel insulating film are trapped at a trap level in the charge storage insulating film. The charges are thus stored in the charge storage insulating film. As a typical charge-trapping nonvolatile semiconductor memory device, a MONOS or SONOS nonvolatile semiconductor storage device is known. A silicon nitride film or the like is used as a material for the charge storage insulating film.
However, for the conventional charge-trapping nonvolatile semiconductor memory devices, both memory cell transistors and select transistors have been insufficiently examined.
Thus, it is conventionally difficult to obtain an excellent semiconductor device in which both the memory cell transistors and the select transistors exhibit proper characteristics.